Segmented prism element and associated methods for manifold fiberoptic switches

ABSTRACT

A fiber optic switch utilizing a segmented prism element, comprising a fiber optic switch used in multi-channel optical communications networks and having one or more arrays of micro electromechanical system (MEMS) mirrors, wherein at least a first array of MEMS mirrors is utilized to select &amp; switch wavelengths from a number of input fiber ports (N) to an output fiber port, wherein at least a second array of MEMS mirrors using and sharing the same free space optics as the first MEMS array is utilized to produce yet another fiber optic switch, wherein the second switch is utilized to select individual wavelengths or spectral components from its input fiber ports to send to its output fiber port for optical power or other monitoring purposes, thus, enabling a cost effective, high level of integration N×1 or alternatively a 1×N switch capable of internal feedback monitoring.

PRIORITY CLAIM TO RELATED US APPLICATIONS

To the full extent permitted by law, the present United StatesNon-Provisional patent application claims priority to and the fullbenefit of United States Provisional patent application entitled“Segmented Prism Element and Associated Methods for Manifold FiberopticSwitches,” filed on Nov. 7, 2006, having assigned Ser. No. 60/857,441,incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to all-optical fiber opticcommunications and datacom switches, and more specifically pertains tofiber optic switches used in multi-wavelength networks.

BACKGROUND

Modern communications networks are increasingly based on silica opticalfiber which offers very wide bandwidth within several spectralwavelength bands. At the transmitter end of a typical point-to-pointfiber optic communications link an electrical data signal is used tomodulate the output of a semiconductor laser emitting, for example, inthe 1525-1565 nanometer transmission band (the so-called C-band), andthe resulting modulated optical signal is coupled into one end of thesilica optical fiber. On sufficiently long links the optical signal maybe directly amplified along the route by one or more amplifiers, forexample, optically-pumped erbium-doped fiber amplifiers (EDFAs). At thereceiving end of the fiber link a photodetector receives the modulatedlight and converts it back to its original electrical form. For verylong links the optical signal risks becoming excessively distorted dueto fiber-related impairments such as chromatic and polarizationdispersion and by noise limitations of the amplifiers, and may bereconstituted by detecting and re-launching the signal back into thefiber. This process is typically referred to asoptical-electrical-optical (OEO) regeneration.

In recent developments, the transmission capacity of fiber optic systemshas been greatly increased by wavelength division multiplexing (WDM) inwhich multiple independent optical signals, differing uniquely bywavelength, are simultaneously transmitted over the fiber optic link.For example, the C-band transmission window has a bandwidth of about 35nanometers, determined partly by the spectral amplification bandwidth ofan EDFA amplifier, in which multiple wavelengths may be simultaneouslytransmitted. All else being equal, for a WDM network containing a numberN wavelengths, the data transmission capacity of the link is increasedby a factor of N. Depending on the specifics of a WDM network thewavelength multiplexing into a common fiber is typically accomplishedwith devices employing a diffraction grating, an arrayed waveguidegrating, or a series of thin-film filters. At the receiver of a WDMsystem, the multiple wavelengths can be spatially separated using thesame types of devices that performed the multiplexing and thenseparately detected and output in their original electrical datastreams.

Dense WDM (DWDM) systems are being designed in which the transmissionspectrum includes 40, 80, or more wavelengths with wavelength spacing ofless than 1 nanometer. Current designs have wavelength spacing ofbetween 0.4 and 0.8 nanometer, or equivalently a frequency spacing of 50to 100 GHz respectively. Spectral packing schemes allow for higher orlower spacing, dictated by economics, bandwidth, and other factors.Other amplifier types, for example Raman, that help to expand theavailable WDM spectrum are currently being commercialized. However, thesame issues about signal degradation and OEO regeneration exist for WDMas with non-WDM fiber links. The expense of OEO regeneration iscompounded by the large number of wavelengths present in WDM systems.

Modern fiber optic networks are evolving to be much more complicatedthan the simple point-to-point “long haul” systems described above.Instead, as fiber optic networks move into the regional, metro, andlocal arenas they increasingly include multiple nodes along the fiberspan, and connections between fiber spans (e.g., mesh networks andinterconnected ring networks) at which signals received on one incominglink can be selectively switched between a variety of outgoing links, ortaken off the network completely for local consumption. For electroniclinks, or optical signals that have been detected and converted to theiroriginal electrical form, conventional electronic switches directlyroute the signals to their intended destination, which may then includeconverting the signals to the optical domain for fiber optictransmission. However, the desire to switch fiber optic signals whilestill in their optical format, thereby avoiding expensive OEOregeneration to the largest extent possible, presents a new challenge tothe switching problem. Purely optical switching is generally referred toas all-optical or OOO switching.

Switching

In the most straightforward and traditional fiber switching approach,each network node that interconnects multiple fiber links includes amultitude of optical receivers which convert the signals from optical toelectrical form, a conventional electronic switch which switches theelectrical data signals, and an optical transmitter which converts theswitched signals from electrical back to optical form. In a WDM system,this optical/electrical/optical (OEO) conversion must be performed byseparate receivers and transmitters for each of the W wavelengthcomponents on each fiber. This replication of expensive OEO componentsis currently slowing the implementation of highly interconnected meshWDM systems employing a large number of wavelengths.

Another approach for fiber optic switching implements sophisticatedwavelength switching in an all-optical network. In a version of thisapproach that may be used with the present invention, the wavelengthcomponents W from an incoming multi-wavelength fiber are demultiplexedinto different spatial paths. Individual and dedicated switchingelements then route the wavelength-separated signals toward the desiredoutput fiber port before a multiplexer aggregates the optical signals ofdiffering wavelengths onto a single outgoing fiber. In conventionalfiber switching systems, all the fiber optic switching elements andassociated multiplexers and demultiplexers are incorporated into awavelength cross connect (WXC), which is a special case of an enhancedoptical cross connect (OXC) having a dispersive element andwavelength-selective capability. Additionally, such systems incorporatelenses and mirrors which focus light to a single focal point andlenslets which collimate such light.

Advantageously, all the fiber optic switching elements can beimplemented in a single chip of a micro electromechanical system (MEMS).The MEMS chip generally includes a two-dimensional array of tiltablemirrors which may be separately controlled. U.S. Pat. No. 6,097,859 toSolgaard et al., incorporated herein in its entirety, describes thefunctional configuration of such a MEMS wavelength cross connect whichincorporates a wavelength from an incoming fiber and is capable ofswitching wavelength(s) to any one of multiple outgoing fibers. Theentire switching array of several hundred micro electromechanical system(MEMS) mirrors can be fabricated on a chip having dimension of less thanone centimeter by techniques well developed in the semiconductorintegrated circuit industry.

Solgaard et al. further describes a large multi-port (including multipleinput M and multiple output N ports) and multi-wavelength WDMcross-connect switch (WXC) accomplishing this by splitting the WDMchannels into their wavelength components W and switching thosewavelength components W. The Solgaard et al. WXC has the capability ofswitching any wavelength channel on any input port to the correspondingwavelength channel on any output fiber port. Again, a wavelength channelon any of the input fibers can be switched to the same wavelengthchannel on any of the output fibers.

A complex WDM or white-light network is subject to many problems. Forexample, the different optical signals which are propagating on aparticular link or being optically processed may have originated fromdifferent sources across the network. Also, in a WDM system, the WDMwavelength output power may vary from transmitter to transmitter becauseof environmental changes, aging, or differences in power injected intothe WDM stream. Different optical sources for either a WDM orwhite-light system are additionally subject to different amounts ofattenuation over the extended network. Particularly, for awavelength-routed transparent network, the WDM spectrum on a given fibercontains wavelength components which generally have traversed manydiverse paths from different sources and with different losses anddifferent impairment accumulation, such as degradation of the opticalsignal-to-noise ratio or dispersion broadening. Further, wavelengthmultiplexing and demultiplexing usually rely on optical effects, such asdiffraction or waveguide interference, which are very sensitive toabsolute wavelength, and which cannot be precisely controlled.Additionally, the prior art is disadvantageously limited to complexmulti input and output fiber port, single dedicated wavelength channelMEMS mirrors, and multi wavelength WDM cross-connect switches.

EDFAs or other optical amplifiers may be used to amplify optical signalsto compensate loss, but they amplify the entire WDM signal and theirgain spectrum is typically not flat. Therefore, measures are needed tomaintain the power levels of different signals at common levels or atleast in predetermined ratios.

Monitoring

Monitoring of the WDM channels is especially important in opticaltelecommunication networks that include erbium doped fiber amplifiers(EDFAs), because a power amplitude change in one channel may degrade theperformance of other channels in the network due to gain saturationeffects in the EDFA. Network standard documents, such as the BellcoreGR-2918, have been published to specify wavelength locations, spacingand signal quality for WDM channels within the networks. Networkperformance relative to these standards can be verified by monitoringwavelength, power and signal-to-noise ratio (SNR) of the WDM channels.

A multi-wavelength detector array or spectrometer may be integrated intothe free space of a WXC and utilized to monitor wavelength channels,power and signal-to-noise ratio (SNR) in telecommunication networks.Typically, a portion of the WDM channels are diverted by a splitter orpartially reflective mirror to an optical power monitor or spectrometerto enable monitoring of the WDM channels. Each MEMS mirror in today'sWDM cross-connect switch is dedicated to a single wavelength channel.Whether it tilts about one or more axes, such mirror may be used tocontrol the amount of optical power passing through WXC for such singlewavelength channel. In addition, a detector array or spectrometer may beexternal to the free space of the WXC or OXC, and may be utilized tomonitor white light (combined wavelength channels) power, andsignal-to-noise ratio of optical signal via input/output fiber port tapsor splitters. More specifically, the prior art consists of costly largetwo-dimensional detector arrays or spectrometer utilized to monitormultiple input or output wavelength channels, power and signal-to-noiseratio.

Monitoring and switching are part of a feedback loop required to achieveper-wavelength insertion loss control and such systems comprise threeclassic elements: sensor for monitoring, actuator for multi wavelengthswitching and attenuating, and processor for controlling wavelengthswitching, selection and equalization. The actuator in today's WXCproducts is typically a MEMS-based micromirror or a liquid crystalblocker or reflector. The sensor is typically a modular optical powermonitor, comprising a mechanical filter for wavelength selection and aphotodetector. Depending on the system, the three elements can beco-located in the same device, or can exist as separate standalone cardsconnected by a backplane.

In general, higher levels of integration of the sensor, actuator, andprocessor are attractive from a size, cost, speed, and simplicity ofoperation standpoint. The proposed new solution reaps these benefitsbecause of a very high level of integration.

Therefore, it is readily apparent that there would be a recognizablebenefit from a cost effective fiber optic switch with dual channelselector for all-optical communication networks in which each switchingnode demultiplexes the aggregate multi-wavelength WDM signal from inputfibers into its wavelength components, spatially switches one of manysingle-wavelength components from different input fibers for eachwavelength channel, and wherein such switch multiplexes the switchedwavelength components to one output fiber for retransmission; andwherein such wavelength components power may be monitored and varied bycontrollable attenuation, resulting in a higher level of integration ofthe sensor, actuator, and processor and enabling multiple switches in asingle device capable of utilizing common optical components.

BRIEF DESCRIPTION

Briefly described in a preferred embodiment, the present inventionovercomes the above-mentioned disadvantages and meets the recognizedneed for such an invention by providing a fiber optic switch utilizing asegmented prism element comprising a fiber optic switch used inmulti-channel optical communications networks and having one or morearrays of micro electromechanical system (MEMS) mirrors, wherein atleast a first array of MEMS mirrors utilized to select and switchwavelengths from a number of input fiber ports (N) to an output fiberport (M), and wherein λn from multiple fiber ports (N) is focused on λnmirror via the use of such segmented prism element, wherein at least asecond array of MEMS mirrors using and sharing the same free spaceoptics as the first MEMS array is utilized to produce yet another fiberoptic switch, wherein the second switch is utilized to select individualwavelengths or spectral components from its input fiber ports to send toits output fiber port for optical power or other monitoring purposes,thus, enabling a cost effective, high level of integration N×1, oralternatively a 1×N switch capable of internal feedback monitoring anddynamic insertion loss control of a switching node in telecommunicationnetworks.

According to its major aspects and broadly stated, the present inventionin its preferred form is a fiber optic switch enabled by the segmentedprism element (SPE), comprising input fiber ports, free space optics(FSO) (including but not limited to various lenses, a diffractiongrating for spatially separating/combining the wavelength components ofthe aggregate multi-wavelength WDM signal, and the SPE), a first arrayof MEMS mirrors whose individual mirrors correspond to uniquewavelengths operating within the WDM network (for example, mirror #1corresponding to λ #1 and receiving λ #1 from all input fiber ports,wherein by tilting MEMS mirror #1, the preferred optical path isgenerated via beam steering between an input fiber port and the outputfiber port of the N×1 configuration, this being repeated independentlyfor every wavelength in the WDM network and for every MEMS mirror),wherein such switch multiplexes the MEMS-steered wavelength componentsfrom various input fiber ports to one output fiber port forre-transmission in the WDM network, and wherein the above switchingfunctionality, whether in duplicate or variation thereof, is repeatedone or more times within the same physical switching device (i.e.,common housing) using one or more additional arrays of MEMS mirrorswhile simultaneously sharing the other free space optic (FSO) componentsdescribed above. Analogously, the light direction may be arbitrarilyreversed from the above description so that wavelengths may be switchedfrom a single input fiber port to any of a number of output fiber ports(1×N) without restriction on which wavelength is routed to which outputport. Alternatively, there may be a mixture of multiple input fiberports and multiple output fiber ports, with the restriction that therecannot be an arbitrary switching assignment of input ports to outputports for any given wavelength.

Accordingly, a feature and advantage of the present invention is itsability to focus wavelength components from any or all of the inputfiber ports onto a single MEMS mirror, enabling such mirror to selectthe input port wavelength component to be switched to the output fiberport in an N×1 switch, and to do so for manifold switches operatingindependently and in parallel while sharing all FSO components withinthe same physical housing.

Another feature and advantage of the present invention is its ability tofocus wavelength components from the input fiber ports onto MEMSmirrors, enabling such mirror to select the output fiber port wavelengthcomponent to be switched to the output fiber port in a 1×N switch bysimple rotation or tilt of the mirror, wherein the MEMS mirrors are onlyrequired to tilt around a single common axis of rotation in order toexecute switching commands.

Still another feature and advantage of the present invention is itsability to provide one or more taps or splitters for coupling power frominput and/or output fiber ports.

Yet another feature and advantage of the present invention is itsability to utilize switches to provide monitoring input fiber portsutilized to receive tapped or other multi-wavelength WDM signals for thepurpose of optical power or other quality-of-signal measurements.

Yet another feature and advantage of the present invention is itsability to reuse the same free space optics (various lenses, adiffraction grating for spatially separating/combining the wavelengthcomponents of the aggregate multi-wavelength WDM signal, and the SPE)for manifold switches existing in the same physical housing.

Yet another feature and advantage of the present invention is itsability to provide an optical path between manifold switches (i.e., anoptical bridge) to create a form of M×N switch, wherein in a preferredembodiment the optical bridge may be formed with a simple mirror placedat the SPE between two switches in the manifold switch.

Yet another feature and advantage of the present invention is itsability to provide for ganged switching functionality of the manifoldswitch, wherein the MEMS mirrors corresponding to a certain WDMwavelength are tilted synchronously between all arrays of MEMS mirrorsin the manifold switch, wherein the same switch state is created for allswitches in the manifold switch on a per wavelength basis.

Yet another feature and advantage of the present invention isflexibility wherein an almost limitless range of configurations may beobtained, wherein configuration variations may include number of inputand output fiber ports, number of switches in the manifold, gangedswitching operations, bridging between switches in the manifold, numberand spacing of wavelengths in the WDM system, and the like.

Yet another feature and advantage of the present invention is itsability to be calibrated such that systematic effects are canceled andthe switching performance improved, wherein systematic effects to becanceled may include, for example, imperfect MEMS mirrors, assembly andcomponent imperfections, environmental effects, and the like, andwherein the obtained calibration data is stored in an electronic memorythat can be accessed in real-time in support of switching control andcommand.

Yet another feature and advantage of the present invention is itsability to utilize a second array, or more, of MEMS mirrors forselecting one wavelength component from any of the wavelength componentsof any of the tapped ports for each wavelength of the multi-wavelengthWDM signal, and wherein such switch directs the selected wavelengthcomponent to one monitoring output fiber port for optical powermonitoring.

Yet another feature and advantage of the present invention is itsability to provide more MEMS mirrors in an array than there arewavelengths in the WDM network such that various spectralcharacteristics of the aggregate multi-wavelength WDM signal may bemeasured when utilizing the switching functionality for monitoringpurposes. For example, by placing MEMS mirrors between the mirrorsdesignated for WDM wavelengths a measure of inter-wavelength noise canbe obtained, leading to a form of signal-to-noise measurement. Further,by adding even more mirrors to the MEMS array the spectral location ofthe various multi-wavelength components of the WDM signal may beverified, leading to a form of absolute wavelength measurement.

Yet another feature and advantage of the present invention is itsability to utilize a multi-mode fiber in the fiber array leading to thephotodetector when utilizing the switching functionality for monitoringpurposes, wherein the larger core of a multimode fiber increases theconfidence that the true power of the intended measurement is beingcaptured with sufficient margin for MEMS mirror pointing errors,environmental and aging effects, and the like, wherein the coupling oflight from free space into a fiber is vastly less sensitive topositional errors for a multi-mode fiber than for the single-mode fiberstypically used for telecom/datacom networks.

Yet another feature and advantage of the present invention is itsability, during signal monitoring, to record the power levels duringsignal measurement as the associated MEMS mirror is swept through arange of angle on either side of the expected peak power coupling angle,wherein the peak signal recorded during this sweep, or the peak of acurve-fit through the data points so taken, represents the truestmeasure of the intended signal, wherein the detected peak signal ismaximally isolated from the potentially detrimental effects of MEMSmirror pointing errors, environmental and aging effects of the system,and the like, wherein this sweep and peak-detect approach is aided bythe use of a multi-mode fiber in the fiber array leading to thephotodetector.

Yet another feature and advantage of the present invention is itsability to provide one or more fiber ports carrying aggregatemulti-wavelength WDM signals for the purpose of monitoring said WDMsignals, wherein the origin of the WDM signals is arbitrary.

Yet another feature and advantage of the present invention is itsability to self-monitor the aggregate multi-wavelength WDM signals atthe input and/or output fiber ports of a manifold switch.

Yet another feature and advantage of the present invention is itsability to monitor signals within fibers, wherein signals to bemonitored may be produced by wideband optical power taps placed on thefibers to be monitored, wherein other approaches make only approximatemeasurements of signals by sampling them in free-space and thereforeneglecting free-space-to-fiber coupling effects.

Yet another feature and advantage of the present invention is itsability, with regard to signal monitoring, to be calibrated such thatsystematic effects are canceled and the measurement accuracy increased,wherein systematic effects to be canceled may include the path-dependentinsertion loss of various optical paths through the system, imperfectMEMS mirrors, tap device characteristics, assembly and componentimperfections, environmental effects, and the like, wherein so obtainedcalibration data is stored in an electronic memory that can be accessedin real-time in order to provide corrections to signal measurements inreal-time.

Yet another feature and advantage of the present invention is itsability to utilize the measurement of power levels of WDM wavelengthsobtained via the described self-monitoring functionality as a form offeedback to the 1×N or N×1 switch, wherein the insertion loss of eachwavelength through the switch may be actively adjusted to correct formirror tilt errors, environmental effects, and the like, or similarly toproduce desired spectral distributions of the aggregate multi-wavelengthWDM signals (for example, making the power levels of all wavelengthsequal via the selective attenuation of every wavelength), wherein theinsertion loss of each wavelength is controlled by the tilting of theassociated MEMS mirror in the 1×N or N×1 mirror array, wherein tiltingthe MEMS mirror away from its optimal angle of lowest insertion losssteers the free space beam arriving at the output port(s) and thereforemisaligns the beam with respect to the output fiber port(s) andintroduces progressively larger insertion loss as the MEMS mirror isfurther tilted.

Yet another feature and advantage of the present invention is itscompatibility with using MEMS mirrors that can tilt around 2 independentaxes of rotation, wherein the primary tilt axis is required forfiber-to-fiber switching and the secondary tilt axis my be used forauxiliary purposes, wherein such auxiliary uses of the secondary tiltaxis may include insertion loss control, correction of component andassembly imperfections, environmental and aging effects, and the like.

Yet another feature and advantage of the present invention is itsability to provide a means of power equalization, or other arbitraryspectral power distribution, of wavelengths wherein many beams fromdiverse sources are interchanged among network fibers.

Yet another feature and advantage of the present invention is itsability to provide uniformity of power levels across the WDM spectrum,or other arbitrary spectral distribution, so that dynamic rangeconsiderations at receivers and amplifier, non-linear effects, and crosstalk impairments can be minimized.

Yet another feature and advantage of the present invention is itsability to provide dynamic feedback control since the variouswavelengths vary in intensity with time and relative to changes inoptical channel routing history among the components.

Yet another feature and advantage of the present invention is itsability to provide a fiber optic switch with a means of powerequalization of wavelengths, and thus provide an aggregatemulti-wavelength WDM signal enabling compensation for internalvariations of optical characteristics, misalignments, both integral tothe device and as a result of both manufacturing and environmentalvariation, non-uniformity, aging, and of mechanical stress encounteredin the switch.

Yet another feature and advantage of the present invention is itsability to provide wavelength switching and monitoring in an opticalnetwork while reducing the cost and complexity of such optical network.

Yet another feature and advantage of the present invention is itsapplicability for non-WDM, or “white light” switching devices by thesimple removal of the diffraction grating and the subsequentsimplification of the MEMS array to a single MEMS mirror for eachoptical fiber in the system.

These and other features and advantages of the present invention willbecome more apparent to one skilled in the art from the followingdescription and claims when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present version of the invention will be better understood byreading the Detailed Description of the Preferred and AlternateEmbodiments with reference to the accompanying drawing figures, in whichlike reference numerals denote similar structure and refer to likeelements throughout, and in which:

FIG. 1 is a schematic illustration of a six input port by one outputfiber port wavelength cross-connect (WXC) switch according to anembodiment of the present invention;

FIG. 2 is a schematic illustration of six input port by one output fiberport, dual channel MEMS mirror, output port taps, monitoring input fiberports, monitoring output fiber port, and monitor wavelengthcross-connect switch according to a preferred embodiment of the presentinvention;

FIG. 3A is a schematic illustration of an optical segmented prismelement included in the WXC of FIG. 1;

FIG. 3B is a schematic illustration of an optical segmented prismelement and facet angle equations;

FIG. 4 is a plan view of a single axis tiltable mirror useable with thepresent invention;

FIG. 5A is a functional block diagram of a one input port by five outputfiber port wavelength cross-connect switch with power monitor andfeedback control according to an alternate embodiment of the presentinvention;

FIG. 5B is a functional block diagram of a five input port by one outputfiber port wavelength cross-connect switch with power monitor andfeedback control according to a preferred embodiment of the presentinvention;

FIGS. 6A and 6B are cross sectional views illustrating two kinds ofmismatch in optically coupling a wavelength component beam to thewaveguide substrate according to an alternate embodiment of the presentinvention;

FIG. 7A is a top view of a fiber holder according to a preferredembodiment of the present invention;

FIG. 7B is schematically illustrated optical concentrator array usingplanar waveguide included in the N×1 WXC of FIGS. 1, 2 and 5B accordingto an alternate embodiment of the present invention;

FIG. 7C is schematically illustrated optical concentrator array usingplanar waveguide included in the 1×N WXC of FIG. 5A according to analternate embodiment of the present invention;

FIG. 8 is a schematic view of the front end optics included in the WXCof FIGS. 1 and 2;

FIG. 9A is a front face view of a first illustrative channel MEMS mirrorand five incident beams from the five input fiber ports according to anillustrative embodiment of the present invention;

FIG. 9B is a front face view of a second channel MEMS mirror and twoincident beams from the two monitoring input fiber ports according to anillustrative embodiment of the present invention;

FIG. 9C is a front face view of a third channel MEMS mirror and fiveincident beams from the five input fiber ports according to a preferredembodiment of the present invention as shown in FIG. 12;

FIG. 10 is a schematic illustration of a six input port by one outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 11 is an illustration of a typical single-row MEMS mirror arrayaccording to an embodiment of the present invention;

FIG. 12 is a three-dimensional schematic of a MEMS mirror according toan embodiment of the present invention of FIGS. 9A and 9B;

FIG. 13 is a schematic illustration of a six input port by one outputfiber port wavelength cross-connect switch according to preferredembodiment of the present invention;

FIG. 14 is a three-dimensional schematic of a wavelength cross-connectswitch according to an embodiment of the present invention;

FIG. 15 is a schematic illustration of a wavelength cross-connect withSPE-based architecture for creating manifold switches within the samepackage switch according to an embodiment of the present invention;

FIG. 16 is a schematic illustration of a wavelength cross-connect withSPE-based architecture FCLA-based optics of FIG. 10 according to anembodiment of the present invention;

FIGS. 17A and 17B are schematic illustrations of a 4-input-fiber by4-output-fiber optical switch, made up of four 1×N and four N×1wavelength selectable switches;

FIG. 18A is a schematic illustration of a five input port by one outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 18B is a schematic illustration of an optical segmented prismelement included in the WXC of FIG. 18A;

FIG. 19A is a schematic illustration of a six input port by one outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 19B is a schematic illustration of an optical segmented prismelement included in the WXC of FIGS. 1 and 2, 19A;

FIG. 20 is a schematic illustration of an input port by six output fiberport wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 21 is a schematic illustration of an input port by six output fiberport wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 22A is a schematic illustration of a six input port by six outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention;

FIG. 22B is a schematic illustration of a six input port by six outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention; and

FIG. 23 is a schematic illustration of a six input port by six outputfiber port wavelength cross-connect switch according to an alternateembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED AND SELECTED ALTERNATIVEEMBODIMENTS

In describing the preferred and selected alternate embodiments of thepresent version of the invention, as illustrated in FIGS. 1-23, specificterminology is employed for the sake of clarity. The invention, however,is not intended to be limited to the specific terminology so selected,and it is to be understood that each specific element includes alltechnical equivalents that operate in a similar manner to accomplishsimilar functions.

Referring now to FIG. 1, there is illustrated a schematic illustrationof a six input fiber port by one output fiber port wavelengthcross-connect switch 10. However, it is emphasized that this 6×1embodiment is illustrated only for simplicity, and that by increasingthe number of input fiber ports by N, then an N×1 switch 10 iscontemplated herein, wherein N represents the number of input fiberports. Preferably, wavelength cross-connect switch 10 can be operated ineither direction, wherein N of N×1 represents N input fiber ports andone output fiber port, or one input port and N output fiber ports. Inthe preferred 6×1 wavelength cross-connect switch 10 shown in FIG. 1,six input fiber ports 12, 14, 16, 18, 20, 22, and one output fiber port64 are optically coupled to fiber concentrator array (FCA) 52 (fiberport concentrator), preferably in a linear alignment, wherein preferablyall-fibers (alternatively planar waveguides) 32, 34, 36, 38, 40, 42, and46 are used to bring the respective beams of fiber ports 12, 14, 16, 18,20, 22 and 64 closer together on output face 44 of fiber concentrator 52(fiber port concentrator) adjacent the optics. Further, planarwaveguides 32, 34, 36, 38, 40, 42, 46 are also preferably used to outputthe beams in parallel in a predominantly linearly spaced grid whereinplanar waveguides 32, 34, 36, 38, 40, 42 have curved shapes within fiberconcentrator 52 and are optically coupled to input fiber ports 12, 14,16, 18, 20, 22. A beam, also known as optical signal, ismulti-wavelength WDM signals and such signals travel in free space,fiber, waveguides, and other signal carriers.

Although, other coupling arrangements are possible, preferred fiberconcentrator 52 offers some additional advantages over other couplingarrangements. For example, its planar waveguides 32, 34, 36, 38, 40, 42concentrate and reduce the spacing between input fiber ports 12, 14, 16,18, 20, 22 from 125 micrometers, representative of the fiber diameters,to the considerably reduced spacing of, for example, 40 micrometers,which is more appropriate for the magnifying optics of switch 10. Eachof waveguides 32, 34, 36, 38, 40, 42 is preferably coupled to therespective 12, 14, 16, 18, 20, 22 input fiber port. Waveguides 32, 34,36, 38, 40, 42 preferably extend along a predominately common planedirecting the multi wavelength signals to output in free space and topropagate in patterns having central axes which are also co-planar.

The free-space beams output by waveguides 32, 34, 36, 38, 40, 42 offiber concentrator 52 are preferably divergent and preferably have acurved field. For simplicity, this discussion will describe all thebeams as if they are input beams, that is, output from fiberconcentrator 52 to free-space optics (FSO) 74. The beams are in fact,optical fields coupled between optical elements. As a result, the verysame principles as those discussed as input beams apply to those of thebeams that are output beams which eventually reenter fiber concentrator52 for transmission onto the network.

The beams output from fiber concentrator 52 into the free space ofwavelength cross-connect switch 10 preferably pass through front endoptics (FE) 56. Outputs of waveguides 32, 34, 36, 38, 40, 42 of face 44preferably are placed at or near the focal point of front end optics 56.Front end optics 56 accepts the light beams coming from or going to allfibers via input and output fiber ports. For light beams emerging from afiber or input port, front end optics 56 preferably captures, projectsand collimates the light in preparation for spectral dispersion bydiffraction grating 62. The reverse of this happens for light beamsconverging toward a fiber; that is, the principles of operation areidentical in either case, and independent of the direction of the light.It should be noted that common diffraction gratings do not operateexactly as shown in FIG. 1, more specifically the input and diffractedbeams do not lie in the same plane as shown in FIG. 1.

Although a single lens is illustrated in FIG. 1, front end optics 56 maygenerally consist of two or more lenses, and may become progressivelysophisticated as the demands of wavelength cross-connect switch 10increases (e.g., the number of fibers, the range of wavelengths, thenumber of input and output fiber ports, the spacing of the MEMS mirrors,etc.). For example, in a two lens front end optics 56, the first lens(closest to the fibers or input fiber ports) may be used to producecustomary flat-field and telecentric beams that easily accommodatesimple fiber arrays or fiber concentrator 52, and the second lens mayperform the majority of the collimation task. As the demands ofwavelength cross-connect switch 10 increase, front end optics 56 mayfurther employ advanced features, such as aspheric optical surfaces,achromatic designs, and the like. Unlike traditional approaches whereina separate lens must be critically aligned to every fiber, front endoptics 56 described herein are preferably common to every fiber, therebyenabling a realization of significant savings in assembly time and costrelative to previously known switch systems.

The collimated beams exiting front end optics 56 propagate substantiallywithin a common plane, and are incident upon diffraction grating 62, awavelength dispersive element, wherein diffraction grating 62 preferablycomprises grating lines extending perpendicular to the principal planeof wavelength cross-connect switch 10. The beams may overlap when theystrike diffraction grating 62, wherein diffraction grating 62 preferablyseparates the input port beams WDM (optical signal) into correspondingsets of wavelength-separated beams, λ1 through λn (wavelengths) for eachinput port beam, where n is the number of wavelengths in each input portbeam. Diffraction grating 62 angularly separates the multi-wavelengthinput beams into wavelength-specific sub-beams propagating in differentdirections parallel to the principal optical plane, or alternativelyserves to recombine single-wavelength sub-beams into a multi-wavelengthbeam. Diffraction grating 62 is preferably uniform in the fiberdirection, wherein the preferred uniformity allows use of diffractiongrating 62 for signals to and from multiple input and output fibers.

The line density of diffraction grating 62 should preferably be as highas possible to increase spectral dispersion, but not so high as toseverely reduce diffraction efficiency. Two serially arranged gratingswould double the spectral dispersion. However, a single grating with aline density of approximately 1000 lines/millimeter has providedsatisfactory performance. Diffraction grating 62 is preferably alignedso that the beam from front end optics 56 has an incident angle ofpreferably 54 degrees on grating 62, and the diffracted angle is about63 degrees. The difference in these angles results in opticalastigmatism, which may be compensated by placing a prism between frontend optics 56 and diffraction grating 62. In brief, the diffractionefficiency of a grating is generally dependent on the characteristics ofthe polarization of the light with respect to the groove direction onthe grating, reaching upper and lower diffraction efficiency limits forlinear polarizations that are parallel p-polarization and perpendiculars-polarization to the grooves.

In addition, polarization sensitivity of the grating may be mitigated byintroducing a quarter-wave plate (not shown) after diffraction grating62 or elsewhere in switch 10 whose optical axis is oriented atforty-five degrees to the diffraction grating limiting diffractionefficiency polarization states described previously. It is contemplatedherein that such quarter-wave plate may be placed elsewhere in switch10. Preferably, every wavelength-separated sub-beam passes twice throughthe quarter-wave plate so that its polarization state is effectivelyaltered from input to output fiber port. That is, diffraction grating 62preferably twice diffracts any wavelength-specific sub-beam, which hastwice passed through the quarter-wave plate. For example, consideringthe two limiting polarization cases the sub-beam passes once with afirst limiting polarization (for example, p-polarization) and once againwith a polarization state that is complementary to the firstpolarization state (for example, s-polarization) from the perspective ofdiffraction grating 62. As a result, any polarization dependenceintroduced by diffraction grating 62 is canceled. That is, the netefficiency of diffraction grating 62 will be the product of its S-stateand P-state polarization efficiencies, and hence independent of theactual polarization state of the input light.

In the wavelength division multiplexing (WDM) embodiments of theinvention, each input fiber port 12, 14, 16, 18, 20, 22 is preferablycapable of carrying a multi-wavelength WDM optical signal havingwavelengths λ1 through λn. Wavelength cross-connect switch 10 ispreferably capable of switching the separate wavelength components fromany input port to planar waveguide 46 of fiber concentrator 52, which ispreferably coupled to output fiber port 64. This architecture applies aswell to a WDM reconfigurable add/drop multiplexer (ROADM), such as a 1×6ROADM in which fiber ports 12, 14, 16, 18, 20, 22 are associatedrespectively with the input (IN) (fiber port 12), five (5) DROP ports(fiber ports 14, 16, 18, 20, 22), and output (OUT) (fiber port 64). Or,in the 6×1 ROADM, input (IN) (fiber port 12), five (5) ADD ports (fiberports 14, 16, 18, 20, 22), and output (OUT) (fiber port 64). Inoperation, fiber ports 14, 16, 18, 20, 22, (local ports) are switchedto/from by wavelength cross-connect switch 10, either are added (ADD) tothe aggregate output (OUT) port 64 or dropped (DROP) from the aggregateinput (IN) port 12.

Back end optics (BE) 66 projects the wavelength-separated beams ontosegmented prism element (SPE) 68 (steering element). Back end optics 66creates the “light bridge” between diffraction grating 62 and segmentedprism element 68 to switching mirror array 72. Considering the case oflight diffracting from diffraction grating 62 and traveling toward backend optics 66, such back end optics 66 preferably capture the angularly(versus wavelength) separated beams of light, which is made plural bythe number of fibers, and wherein back end optics 66 create parallelbeams of light. The parallel beams are obtained via a preferredtelecentric functionality of back end optics 66. In addition, becauseall beams are preferably at focus simultaneously on the flat MEMS planeof switching mirror array 72, then back end optics 66 must alsopreferably perform with a field-flattening functionality. After lightreflects off of a MEMS mirror and back into back end optics 66, thereverse of the above occurs; the principles of operation are identicalin either case and are independent of the direction of the light.

Although a single lens is illustrated in FIG. 1, back end optics 66 maygenerally consist of two or more lenses or mirror, and may becomeprogressively sophisticated as the demands of wavelength cross-connectswitch 10 increases (e.g., the number of fibers, the range ofwavelengths, the number of input and output fiber ports, the spacing ofthe MEMS mirrors, etc.). The focal length of back end optics 66 (or theeffective focal length in the case of multiple lenses) is preferablydetermined from the rate of angular dispersion versus wavelength ofdiffraction grating 62 and the desired mirror spacing of switchingmirror array 72. If the angular separation between two neighboringwavelengths is denoted by A and the spacing between their associatedMEMS micro-mirrors is denoted by S, then the focal length of back endoptics 66 (F) is approximated by F=S/tan(A). Because the angulardispersion of common gratings is relatively small, and/or as thespectral separation between neighboring wavelengths is decreased, thenback end optics 66 focal length may become relatively large. Preferably,however, a physically compact optical system may be retained byproviding back end optics 66 with a telephoto functionality, therebyreducing the physical length of back end optics 66 by a factor of two ormore. A three-lens system is generally sufficient to provide all of thefunctionalities described above, and the lenses themselves can becomeincreasingly sophisticated to include aspheric surfaces, achromaticdesign, etc., as the demands of wavelength cross-connect switch 10increase (e.g., depending on the number of fibers, the range ofwavelengths, the number of input and output fiber port, the spacing ofthe MEMS mirrors, etc.). The focal length calculations set forth herewith respect to the back end optics are applicable to the front endoptics as well.

Such a preferred multi-lens back end optics 66 system, by virtue of itsincreased degrees-of-freedom, additionally allows for active opticaladjustments to correct for various lens manufacturing tolerances andoptical assembly tolerances that otherwise would not be available.Segmented prism element 68, although physically existing in the beampath of back end optics 66, is preferably designed utilizing passivemonolithic element containing multiple prism or lenses and preferablyfunctions almost independently of back end optics 66.

Referring now to FIG. 3A, there is illustrated a schematic illustrationof a preferred optical segmented prism element included in the WXC ofFIG. 1 (the number of segments or facets varies with the number ofsignals present in the WXC). Segmented prism element 68 preferablyrefracts wavelength-separated beams from back end optics 66 and steerssuch beams onto switching mirror array 72 based on the refractiveindices of each segment. Segmented prism element 68 (steering element)preferably refracts λn from each input port 12, 14, 16, 18, 20, 22 ontoλn mirror of switching mirror array 72 assigned to λn. For example, λ1mirror of switching mirror array 72 has λ1(12)-λ1(22) from all inputfiber ports 12-22 projected onto λ1 mirror surface via segmented prismelement 68, and by titling λ1 mirror of MEMS switching mirror array 72,wavelength cross-connect switch 10 preferably switches one selected λ1(12-22) from input fiber ports 12-22 to output fiber port 64 and blocksthe remaining unselected λ1(s) from input fiber ports 12-22, and soforth for λ2-λn. Each λn mirror of switching mirror array 72, in thisexample, has five input beams projected simultaneously onto the surfaceof such mirror, all at wavelength λn, wherein those five beams arepreferably demultiplexed and focused by free space optics 74 from inputfiber ports 12, 14, 16, 18, 20. It should be recognized that utilizingsegmented prism element 68 enables refracting and/or steering ofmultiple wavelengths onto a single mirror from one or more input fiberports 12-22 or refracting light to any arbitrary point rather than priorart switches, which use lenses or mirrors to focus individualwavelengths to individual dedicated mirrors based on one focal point.Further, it should be recognized that utilizing segmented prism element68 enables multiple N×1 switches to be packaged as a single unit. Stillfurther, it should be recognized that utilizing segmented prism element68 enables the potential elimination of lenslets for each optical fiberport, thereby reducing the number of elements and the overall cost ofthe switch.

Segmented prism element 68 preferably is manufactured from fine-annealglass with class-zero bubble imperfections whose facets are very finelypolished and are coated with anti-reflection material. Further, the typeof glass may be chosen to have certain optical properties at the desiredwavelengths of operation, including but not limited to opticaltransparency and refractive index. The angular deflection imparted byeach facet of segmented prism element 68 is preferably a function ofboth the angle of the facet and the refractive index of the glass asshown in FIG. 3B—Segmented Prism Element 68 “Light Deflection Principlesand Equations”; hence, in principle segmented prism element 68 can bemade from a wide variety of glass types. This allows furtheroptimization of the glass material per the criteria of cost, ease offabrication, etc. As an example, the type of glass known as BK7 is acommon high-quality, low cost glass that is preferably suitable for thisapplication.

Another criterion for glass selection may be its change in opticalproperties relative to temperature. Since the refractive index of allmaterials changes with temperature, which could in turn produceundesirable changes in the effective facet angles 102 produced bysegmented prism element 68, then for demanding applications, a glasswith a very low thermo-optic coefficient may be chosen at the desiredoperational temperature range. For example, the common glasses known asK5 and BAK1 have very low thermo-optic coefficients at room temperature.In addition to the precision polishing of the segmented prism element 68from bulk glass, segmented prism element 68 may also be fabricated usingcastable glass materials, such as sol-gel. Prism elements fabricated insuch fashion should exhibit improved performance consistency comparedwith those fabricated using traditional polishing techniques. Thematerials for fabrication of segmented prism element 68 are not limitedto glass but may also include high quality plastic materials such asZEONEX (Zeon Chemicals L.P.). As such, the cost of manufacturingsegmented prism element 68 may be further lowered by using plasticinjection molding techniques.

An alternative to fabricating segmented prism element 68 from a singlemonolithic piece of glass or plastic is to fabricate each facet section,and/or groups of facet sections, individually and then vertically stackthem to create a single composite element.

In a preferred embodiment, segmented prism element 68 is polished frombulk BK7 glass and has dimensions of length 40 millimeters, height 15millimeters, width at the base of 4 millimeters and width at the top of3.18 millimeters. Facet angles 102 for the six input fiber wavelengthsand one output fiber wavelength model preferably are 11.82, 8.88, 5.92,2.96, 0.00, −2.96, −5.92 degrees. For ease of fabrication so that theedges of adjacent facets are coincident, especially with regard tofabrication by polishing, segmented prism element 68 preferably isdesigned to have varying degrees of thickness for each facet, resultingin the above stated angles of deflection, wherein such angles ofdeflection preferably position the six input λ1(12)-λ1(22) wavelengthson λ1 mirror and so on for λ2-λn mirrors. It should be noted, however,that segmented prism element 68 may be designed and manufactured havingfacet angles 102 different than set forth herein, depending on the fiberspacing, number of input fiber ports, number of wavelength componentsper input port, lenses, grating, MEMS mirror configuration, and thelike.

Referring again to FIG. 1, the distance between switching mirror array72, segmented prism element 68, and the vertical location of the beam atsegmented prism element 68, and free space optics 74 as well as otherfactors including fiber spacing, number of input fiber ports, number ofwavelength components per input port, lenses, grating, MEMS mirrorconfiguration and output fiber ports preferably determines the facetangle required to enable all six input port wavelengths to be positionedon each MEMS mirror assigned to the specific wavelength of switchingmirror array 72. Because the vertical location of the various fiber portcomponents are different as they intercept the segmented prism element68, the facet angles of segmented prism element 68 preferably varyaccordingly in order to combine all of wavelengths λn at a common mirrorλn of switching mirror array 72. The analogous situation exists for theselected input port wavelength λn reflecting from mirror λn of switchingmirror array 72 directed to output fiber port 64. This is illustrated inFIG. 3B, and wherein the facet angle A can be determined from equationβ. In finding the preferred facet angle A from equation β, the knownvariables are the input beam angle, α, the distance between the inputbeam vertical location at segmented prism element 68 relative to mirrorλn of switching mirror array 72, y, and the distance between thesegmented prism element 68 and the MEMS, z, leaving the only freevariable as the refractive index material of segmented prism element 68(η). Equation β is transcendental in A and may be solved by iteration orvarious algorithms.

Referring now to FIG. 4, there is illustrated a top view of a singleaxis tiltable (moveable) mirror. Switching mirror array 72 (as seen inFIGS. 1 and 2) is preferably formed as a two-dimensional array(preferably two rows of 40 mirrors) of single-axis tiltable mirrors,with one mirror, single cell (mirror) 260 of switching mirror array 72.Cell 260 is one of many such cells arranged typically in atwo-dimensional array in a bonded structure including multiple levels ofsilicon and oxide layers in what is referred to as multi-levelsilicon-over-insulator (SOI) structure. Cell 260 preferably includesframe 262 supported in support structure 264 of switching mirror array72. Cell 260 further includes mirror plate 268 having reflective surface270 twistably supported on frame 262 by a pair of torsion beams 266extending from frame 262 to mirror plate 268 and twisting about axis274. In one MEMS fabrication technique, the illustrated structure isintegrally formed in an epitaxial (epi) layer of crystalline silicon.The process has been disclosed in U.S. Provisional Application Ser. No.60/260,749, filed Jan. 10, 2001, (now abandoned) is incorporated hereinby reference in its entirety. However, other fabrication processesresulting in somewhat different structures may be used without affectingor departing from the intended scope of the present invention.

Mirror plate 268 is controllably tilted about axis 274 in one dimensionby a pair of electrodes 272 under mirror plate 268. Electrodes 272 aresymmetrically disposed as pairs across axis 274 respective torsion beams266. A pair of voltage signals V(A), V(B) is applied to the two mirrorelectrodes 272, while a common node voltage signal V(C) is applied toboth mirror plate 268 and frame 262.

Circumferentially lateral extending air gap 278 is preferably definedbetween frame 262 and mirror plate 268 so that mirror plate 268 canrotate with respect to frame 262 as two parts. Support structure 264,frame 262, and mirror plate 268 are driven by the common node voltageV(C), and electrodes 272 and mirror plate 268 form plates of a variablegap capacitor. Although FIG. 4 illustrates the common node voltage V(C)being connected to mirror plate 268, in practice, the electrical contactis preferably made in support structure 264 and torsion beams 266 applythe common node voltage signal to both frame 262 and mirror plate 268,which act as a top electrode. Electrical connectivity between frame 262and mirror plate 268 can be achieved through torsion beams 266themselves, through conductive leads formed on torsion beams 266, orthrough a combination of the two. Electrodes 272 are formed under mirrorplate 268 and vertical air gap 279 shown into the page is furtherdefined between electrodes 272 and mirror plate 268 and forms the gap ofthe two capacitors.

Torsion beams 266 act as twist springs attempting to restore mirrorplate 268 to its neutral tilt position. Any voltage applied acrosseither electrode 272 and mirror plate 268 exerts an attractive forceacting to overcome torsion beams 266 and to close the variable gapbetween electrodes 272 and mirror plate 268. The force is approximatelylinearly proportional to the magnitude of the applied voltage, butnon-linearities exist for large deflections. The applied voltage can bea DC drive or an AC drive per Garverick et al. set forth below. Inpractice, the precise voltages needed to achieve a particular tilt areexperimentally determined.

Because each of two electrodes 272 forms a capacitor with mirror plate268, the amount of tilt is determined by the difference of the RMSvoltages applied to the two capacitors of the pair. The tilt can becontrolled in either direction depending upon the sign of the differencebetween the two RMS voltages applied to V(A) and V(B).

Referring again to FIG. 1, there are many ways of configuring the MEMSarray of micromirrors and their actuation as wavelength switching array(WSA) 75. The following is an example: The MEMS array may be bonded toand have an array of solder bumps contacting it to control circuitry 78,preferably including high-voltage circuitry needed to drive theelectrostatic actuators associated with each of the mirrors. Controlcircuitry (controller) 78 controls the driver circuit and hence themirrors in a multiplexed control system including address lines, datalines, and a clock line, driven in correspondence to an oscillator. Thecontrol is preferably performed according to pulse width modulation(PWM), a method for controlling the mirror tilt, as Garverick hasdescribed in U.S. Pat. No. 6,543,286, issued Apr. 8, 2003, and U.S. Pat.No. 6,705,165, issued Mar. 16, 2004, incorporated herein by reference intheir entirety. In these methods, a high-voltage square-wave common nodedrive signal is supplied through a power transistor to the commonelectrical node comprising all the mirrors while the driver arraydelivers phase delayed versions of the square-wave signal to eachindividual electrode, the amount of delay determining the RMS voltageapplied across the electrostatic actuator electrodes of each mirror. Inaddition, Garverick has described in U.S. Pat. No. 6,788,981, issuedSep. 7, 2004 and incorporated herein by reference in its entirety, amethod wherein an analog control system for an array of moveablemechanical elements, such as tiltable mirrors, formed in a microelectromechanical system (MEMS) is disclosed.

Control circuitry 78 preferably receives switch commands from theexternal system to effect switching of the wavelength separated channelsbetween the input and output fibers. Preferably, the coarse pointingconstants, which are primarily representative of the physicalcharacteristics of the MEMS array and its driver circuit, may be storedin an electrically programmable read-only memory.

Referring to FIGS. 1 and 4, the angle of a mirror in switching mirrorarray 72 is preferably actively tilted by control circuitry 78 applyinga voltage V(A), V(B) to electrodes 272 of switching mirror array 72 sothat the selected input port sub-beam λn is preferably reflected to landprecisely at the center of concentrator waveguide 46 associated with theparticular output fiber port 64 after retracing its path through freespace optics 74. The mirror is preferably actively tilted by controlcircuitry 78 to the required angle such that the sub-beam, afterreflection off the mirror, is properly aligned to planar waveguide 46associated with output fiber port 64. Preferably, cell 260 (λ1 mirror)assigned to λ1 of switching mirror array 72 tilts its mirror plate 268,which has projected on its reflective surface 270 λ1(12)-λ1(22) from thesix input fiber ports 12-22, and by control circuitry 78 applying apredetermined voltage V(A), V(B) to electrodes 272 of switching mirrorarray 72, tilts mirror plate 268 thereby selecting λ1 from any of thesix input fiber ports 12-22 (the other λ1(s) being not selected arereflected into free space) and the selected λ1 is reflected to landprecisely at the center of planar waveguide 46 associated with outputfiber port 64 after retracing its path through free space optics 74.Wavelength cross-connect switch 10 switches one selected λ1 from inputfiber ports 12-22 to output fiber port 64 and blocks the remainingunselected λ1(s) from input fiber ports 12-22, and so forth for λ2-λn.

The described embodiment was based on 40 channels (n=40) in the˜1530-1562 nanometer band. However, the design is easily adapted toconform to various regions of the optical spectrum, including S-band,C-band, and L-band, and to comply with other wavelength grids, such asthe 100 GHz, 50 GHz, etc. grids published by InternationalTelecommunication Union (ITU).

The described design provides several advantages for facilitating itseasy insertion into WDM systems of either a few wavelengths, or fordense WDM (DWDM) systems having many wavelengths. For example, thedesign of the present invention produces lower polarization modedispersion (PMD) and low chromatic dispersion relative to previousdesigns. Low PMD and chromatic dispersion naturally follows from thefree-space optics.

Other types of MEMS mirror arrays may be used, including dual axisgimbal structure cells, those relying on flexing elements other thanaxial torsion beams, and those moving in directions other than tiltingabout a central support axis. In particular, dual axis gimbaled mirrorsfacilitate hitless switching in regards to 1×N mode of operation.Wavelength dispersive elements other than diffraction gratings also maybe used. The concentrator, although important, is not crucial to many ofthe aspects of the invention. Further, the concentrator may beimplemented in an optical chip serving other functions such asamplification, splitter or wavelength conversion.

A white-light cross connect, that is, an optical switch that switchesall λs on a given fiber together, can be adapted from the system ofFIGS. 1-5 by eliminating the diffraction grating or DeMux/Mux. Althoughthe invention has been described with respect to a wavelength crossconnect, many of the inventive optics can be applied to white-lightoptical cross connects that do not include a wavelength dispersiveelement. Although tilting micromirrors are particularly advantageous forthe invention, there are other types of MEMS mirrors than can beelectrically, magnetically, thermally, or otherwise actuated todifferent positions or orientations to affect the beam switching of theinvention.

Referring now to FIG. 2, a schematic illustration of a six input fiberport by one output fiber port with integrated optical switching andmonitoring system 11 is shown. Optical switching and monitoring system11 preferably includes elements and configuration of switch 10 includingsix input fiber ports 12, 14, 16, 18, 20, 22, additionally auxiliarymonitoring fiber port 23, fiber concentrator array (FCA) 52, planarwaveguides 32, 34, 36, 38, 40, 42, additionally 41, 43 and 45, FSO 74including front end optics (FE) 56, diffraction grating 62, back endoptics (BE) 66, segmented prism element (SPE) 68, switching mirror array72, control circuitry 78, WSA 75, output fiber port 64 and outputmonitoring fiber port 25.

According to a preferred embodiment of the invention, optical switchingand monitoring system 11 is incorporated preferably by fabricatingoutput tap 80 and planar waveguide 41 into fiber concentrator 52,whereby tap 80 preferably couples about 10% of the optical power fromoutput fiber port 64 of planar waveguide 46 into planar waveguide 41which directs the multi wavelength output beam to output in free spaceand propagate in a pattern having a central axis which is co-planar withoutputs from waveguides 32, 34, 36, 38, 40, 42 of FIG. 1 in free spaceoptics 74.

Alternatively, an optical switching and monitoring system with feedbackmonitoring of the output fiber may be implemented externally (off-boardof the optical switching and monitoring system 11) by fusing the outputfiber with an monitoring fiber or via use of face plate connector and asplitter or jumper to couple about 10% of the optical power from outputfiber port 64 fiber into monitoring fiber port 21, which is coupled toplanar waveguide 41. Planar waveguide 41 outputs its multi-wavelengthbeam in free space propagating in a pattern having a central axis whichis co-planar with outputs from waveguides 32, 34, 36, 38, 40 in freespace optics 74.

Optical switching and monitoring system 11 preferably includes auxiliarymonitoring fiber port 23 which is preferably coupled to planar waveguide43, and preferably outputs its multi-wavelength beam in free spacepropagating in a pattern having a central axis which is co-planar withoutputs from waveguides 32, 34, 36, 38, 40, 41, 42, 43 in free spaceoptics 74, thus enabling an auxiliary multi-wavelength beam to bemonitored by optical switching and monitoring system 11. An externalsignal not found on input fiber ports 12, 14, 16, 18, 20, 22 may beinput into auxiliary monitoring fiber port 23 and optical switching andmonitoring system 11 may be utilized to monitor or read the power ofeach wavelength of a multi-wavelength beam input on auxiliary monitoringfiber port 23, and to output such data to a user interface (User i/f)port 77 shown in FIGS. 5A and 5B. It is contemplated herein that morethan one auxiliary monitoring port may be provided in a similar fashion.

Free space optics 74 preferably position the two multi-wavelength beamsof monitoring fiber ports 21 and 23 propagating from planar waveguides42 and 43 onto monitoring mirror array 73 second row (row B). Cell 260assigned to λ1 mirror of monitoring mirror array 73 tilts its mirrorplate 268 (shown in FIGS. 4 and 9B), which has projected on itsreflective surface 270 λ1(21) and λ1(23) from the two monitoring fiberports 21 and 23 and by control circuitry 78 applying a voltage V(A),V(B) to electrodes 272 of monitoring mirror array 73 tilting mirrorplate 268 selects λ1 either from monitoring fiber ports 21 or 23 fromtwo monitoring fiber ports 21 and 23 (the other λ1 being not selected isreflected away from the waveguides) and the selected λ1 is preferablyreflected to land precisely at the center of concentrator waveguide 45associated with the particular output monitoring fiber port 25 afterretracing its path through free space optics 74.

Optical switching and monitoring system 11 is capable of simultaneouslyswitching one selected λ1 from input fiber ports 12-22 to output fiberport 64 and blocking the remaining unselected λ1(s) from input fiberports 12-22, and so forth for λ2-λn, and switching one selected λ frommonitoring fiber ports 21 and 23 to output monitoring fiber port 25 andblocking the remaining unselected λ from monitoring fiber ports 21 or 23as well as all other λs from monitoring fiber ports 21 and 23 and soforth for λ2-λn individually. Output monitoring fiber port 25 preferablyreceives the selected single wavelength λ switched by MEMS mirror array73 (row B) after it has passed through free space optics 74. Outputmonitoring fiber port 25 preferably is coupled to optical power monitor79.

Power monitor (optical measurement device) 79 preferably is aphotodiode, preferably measuring the power level of wavelength λnswitched by monitoring mirror array 73 (row B), measuring one wavelengthat a time. As monitoring mirror array 73 (row B) selects wavelength λnand routes it to waveguide 45 coupled to output monitoring fiber port25, power monitor 79 preferably measures the power of such wavelengthλn. Alternatively, power monitor 79 may be any device capable ofmeasuring power of one or more wavelengths by scanning themulti-wavelength components, as well as analyzing signal to noise ratiosby spectrum analyzing the wavelength bandwidth, polarization-dependentproperties and the like. The optical intensities for allwavelength-separated signals are preferably converted to analog ordigital form by power monitor 79 and supplied to control circuitry 78,which preferably adjusts switching mirror array 72 as set forth hereinto adjust the power of wavelength λn to conform to one or morepredetermined criteria.

Other forms of power monitoring are possible as long as the timenecessary for resolutions of differences in wavelength channel powerlevels is sufficient for power adjustments. If the adjustments areintended to only address aging and environmental effects, the resolvedmeasurement time may be relatively long. On the other hand, fastfeedback may be necessary for initializing switch states, forcompensating for transient changes in power level such as occurs fromthe combination of polarization-dependent loss and polarizationfluctuations which vary at the wavelength level, for stabilizing againstvibration, and for alarm signaling to protection circuitry. Moreover,other parameters may be measured such as optical signal to noise ratio(OSNR), center wavelength, transient behavior, or bit error rate with anappropriate detector.

Moreover, various configurations of optical switching and monitoringsystem 11 are contemplated herein, including taps or splitters for allor a selected number of input and output fiber ports, including theirassociated planar waveguide, free space optics, MEMS mirrors and thelike.

Referring now to FIG. 5A, a functional block diagram of a one input portby five output fiber port 1×N (N=5) optical switching and monitoringsystem 10.1 wavelength cross-connect switch with power monitor andfeedback control is illustrated according to an alternate embodiment ofthe present invention. In optical switching and monitoring system 10.1,forty wavelengths enter input port (In) 12 and are demultiplexed (DeMux)302 into forty separate wavelengths λ1-λ40, the optical cross-connect(OXC) 304 switches the forty wavelengths, multiplexes (Mux) 306, andoutputs the forty wavelengths to their switch selected output (Out 1-5)13, 15, 17, 19, 21. Forty wavelengths in and forty wavelengths out;however, the forty wavelengths out are distributed across the outputfiber ports (Out 1-5) 13, 15, 17, 19, 21 as selected by the opticalcross-connect switch 304. About 10% of the optical power of each output(Out 1-5) 13, 15, 17, 19, 21 is tapped or split off (Output taps) 308 toa 5:1 combiner 310, which is coupled to an 80 channel selector 312.Channel selector 312 preferably selects one wavelength of the fortyinternal or forty external (Aux. OPM In) 23 and feeds such wavelength tothe photo diode (PD) 314. The output from the photodiode is passed tothe equalization control circuit 316 and/or to user interface 77 (Useri/f). The equalization control circuit 316 preferably controls the perwavelength variable optical attenuator (VOA) 318 which adjusts thewavelength transmitted power to conform to one or more predeterminedcriteria. Switch commands 71 are provided by a network management systemor network alarming system external to optical monitoring system 10.1for wavelength selection from input to output switching, for wavelengthselection for power monitoring, and/or power monitoring.

Referring now to FIG. 5B, a functional block diagram of five input fiberports by one output fiber port N×1 (N=5) optical switching andmonitoring system 10.2 wavelength cross-connect switch with powermonitor and feedback control is illustrated according to preferredembodiment of the present invention. In optical switching and monitoringsystem 10.2, forty wavelengths enter each input port (In 1-5) 12, 14,16, 18, 20 and are demultiplexed (DeMux) 304 into five sets of fortyseparate wavelengths λ1-λ40, the optical cross-connect (OXC) 304 selectsand switches forty wavelengths, multiplexes (Mux) 306 and outputs fortyselected wavelengths to output (Out) 64. About 10% of the optical powerof output (Out) 64 is tapped or split off (Output Tap) 308 to an 80channel selector 312. The channel selector 312 selects one wavelength ofthe forty internal or forty external (Aux. OPM In) 23 and feeds suchwavelength to the photo diode (PD) 314. The output from the photodiodeis passed to the equalization control circuit 316 and/or to userinterface 77 (User i/f). The equalization control circuit 316 controlsthe corresponding wavelength variable optical attenuator (VOA) 318 whichadjusts the transmitted power to conform to one or more predeterminedcriteria. Switch commands 71 are provided by a network management systemor network alarming system external to optical monitoring system 10.2for wavelength selection from input to output switching, for wavelengthselection for power monitoring, and/or power monitoring.

User interface 77 preferably is an interface enabling information topass from the optical switching and monitoring system to outside of theoptical switching and monitoring system, and from outside the opticalswitching and monitoring system into the optical switching andmonitoring system, wherein such systems include but are not limited tomanual settings, network management systems and/or network alarmingsystems. Information may include, but is not limited to, wavelengthrouting information, wavelength selection for power monitoring,wavelength to be switched from input to output, switch status,wavelength power levels, wavelength power level settings, and the like.

The optical switching and monitoring systems described above in FIGS. 1,2 and 5 is preferably internal to the optical switching and monitoringsystem and has the advantage of monitoring all the free space optics andmirrors of such switch. However, an external optical monitoring systemis possible wherein photodiode 79 is external and coupled to the opticalswitching and monitoring system via monitoring fiber 25 (shown in FIG.2), with the advantage of monitoring all the optics and mirrors of theswitch, as well the insertion losses between the optical switching andmonitoring system and the network fibers.

Equalization is achieved in the above embodiments with relatively minoradditions to the hardware other than the optical power monitor and taps.Mirrors 72 used for switching between channels and for optimizingtransmission are used additionally for the variable attenuation of theoutput power, thereby effecting variable transmission through opticalswitching and monitoring system 11. To achieve such variable attenuationexternal to the switch would otherwise require separate attenuators ineach of the multiple wavelengths of each of the optical channels.Moreover, the control functions can be incorporated into the samecontrol circuitry 78.

There are two principal types of misalignment or mismatch between thebeam and waveguide to attain variable attenuation of the wavelengthoutput power (transmission coefficient). Referring now to FIG. 6A, across sectional view illustrates a mismatch in optically coupling awavelength component beam to the waveguide substrate according to apreferred embodiment of the present invention. Positional mismatchoccurs when, as illustrated in the cross-sectional view of FIG. 6A,central axis 112 of wavelength λn beam 110 is offset slightly fromcentral axis 114 of waveguide 116 of fiber concentrator 52. The figure,being suggestive only, does not illustrate the smooth variation of theoptical fields both inside and outside of the illustrated wavelength λnbeam 110 and waveguide 116 and across the lateral interface. FIG. 6Afurther assumes that the two modal fields have the same width, which isthe typical object of optical design. Slightly tilting mirror λn ofswitching mirror array 72 (row A) to deliberately misalign or mismatchwavelength λn beam 110 entry into waveguide 116 of fiber concentrator52, resulting in a degraded coupling and in loss of wavelength λn beam110 optical power in waveguide 116. In a typical embodiment, coupling isattenuated by about 1 dB per micrometer of positional mismatch.

On the other hand, angular mismatch occurs when, as illustrated in thecross-sectional view of FIG. 6B, wavelength λn beam 110 is angularlyinclined with respect to waveguide 116 even if their central axes 112and 114 cross at their interface 118. Angular mismatch degrades thecoupling because a phase mismatch occurs between the two fields at theinterface arising from the axial z-dependence of the two complex fields.In a typical embodiment, coupling is degraded by about 1 dB per degreeof angular offset but the angular dependence depends strongly upon theoptics. It should be appreciated that a beam can be both positionallyand angularly mismatched with a waveguide. It should be yet furtherappreciated that the mismatch can occur at the input fiber (if noconcentrator) and its beam field defined by the rest of the opticalsystem.

Referring now to FIG. 7A, there is illustrated a fiber concentrator 120that relies upon optical fiber included in the switch of FIGS. 1, 2 and5. Fiber holder 122 is patterned by precision photolithographictechniques with a series of preferably V-shaped grooves (or otherchannel configuration) in the general planar pattern shown in fiberholder 122 of FIG. 7A. Single-mode or multi-mode optical fibers 124having cores 126 surrounded by claddings 127 and buffer 128. In thisapplication, optical fibers 124 are stripped of their protective buffer128 and cladding 127, or have their cladding 127 reduced or taperedtoward output face 44 of fiber holder 122 to enable close linearplacement of cores 126. Typical core and cladding diameters arerespectively 8.2 micrometers and 125 micrometers. Among other favorableattributes, the concentrated fiber core spacing reduces the amount of“dead space” between fibers which would otherwise increase the totalmirror tilt range. Tapered fibers 124 are preferably placed into thegrooves with their tapered ends forming transition to free-space optics74. The all-fiber design eliminates the tedious alignment and in-pathepoxy joint of combination waveguides, as shown in FIGS. 7B and 7C. Thedesign also eliminates polarization-related effects arising in planarwaveguides.

Fiber concentrator 120 interfaces widely separated optical fibers 124with the closely configured free space optics 74 and wavelengthswitching array 75 of WXC of FIGS. 1 and 2. Multiple fibers 124 aretypically bundled in a planar ribbon. V-shaped grooves in fiber holder122 hold the reduced cladding 128 fibers with a spacing of, for example,40 micrometers. Although a core of each fiber 124 has a relatively smallsize of about 8 micrometers, its outer glass cladding results in a fiberdiameter of approximately 125 micrometers. The large number of fibers,which can be handled by the single set of free-space optics 74 of theinvention, arranged along an optical axis make it difficult to process alarge number of fiber beams with such a large spacing between thembecause the outermost fiber beams are so far from the optical axiscapabilities of the mirrors. Also, as discussed in more detail below, asignificant amount of optical magnification is required between thesefibers and the MEMS mirror array, and the MEMS design and function isgreatly simplified as a result of concentrating the fiber spacing.

Referring now to FIG. 7B, a schematically illustrated optical fiberconcentrator array 52, using planar waveguide included in the 5×1 WXCaccording to a preferred embodiment of the present invention, andincluded in the switch of FIGS. 1, 2 and 5B. Single-mode optical fibers124 having cores 126 surrounded by claddings 127 (shown in FIG. 7A) arebutt coupled to fiber concentrator 52. In the 6×1 switch 10 shown inFIG. 1, six input fiber ports 12, 14, 16, 18, 20, 22 and output fiber 64are preferably optically coupled to fiber concentrator 52 in a linearalignment and are preferably optically coupled to input fiber ports12-22 and output fiber 64 to bring their beams closer together on outputface 44 of fiber concentrator 52 adjacent the optics, and to output thebeams in parallel in a linearly spaced grid. Returning to FIG. 7B, fiberconcentrator 52 preferably has curved shaped planar waveguides 32, 34,36, 38, 40 and 46 corresponding to input fiber ports 12, 14, 16, 18, 20,and output fiber 64 within fiber concentrator 52 to preferablyconcentrate and reduce the spacing between fiber input fiber ports 12,14, 16, 18, 20, 64 from 125 micrometers, representative of the fiberdiameters, to the considerably reduced spacing of, for example 30 or 40,micrometers and preferably no more than 50 micrometers which is moreappropriate for the magnifying optics of switch 10 and an optimum tiltrange of the mirrors. Each of waveguides 32, 34, 36, 38, 40, and 46 ispreferably coupled to respective 12, 14, 16, 18, 20 input port andoutput fiber 64. Further, waveguides 32, 34, 36, 38, 40, 41 and 46preferably extend along a common plane directing the wavelengths tooutput in free space and to propagate in patterns having central axeswhich are also preferably co-planar.

FIG. 7B further discloses the fabricating of output tap 80 and planarwaveguide 41 into fiber concentrator 52, whereby tap 80 preferablycouples about 10% of the optical power from output fiber port 64 ofplanar waveguide 46 into planar waveguide 41, which directs the multiwavelength output beam to output in free space and to propagate in apattern having a central axes which is preferably co-planar with outputsfrom waveguides 32, 34, 36, 38, 40, 46 of FIG. 1 in free space andswitched by monitoring mirror array 73 (row B) after it has passedthrough free space optics 74.

Fiber concentrator 52 may include auxiliary monitoring fiber port 23,coupled to planar waveguide 43, wherein fiber concentrator 52 preferablyoutputs its multi-wavelength beam in free space propagating in a patternhaving a central axis which is preferably co-planar with outputs fromwaveguides 32, 34, 36, 38, 40, 41 in free space optics 74, therebyenabling an external multi-wavelength beam to be monitored by opticalswitching and monitoring system 11. An external signal not found oninput port 12, 14, 16, 18, 20, 22 may be input into auxiliary monitoringfiber port 23 and optical switching and monitoring system 11 may beutilized to monitor or read the power of each wavelength of amulti-wavelength beam on auxiliary monitoring fiber port 23 and tooutput such data to a user interface (User i/f) 77 port shown in FIGS.5A and 5B. It is contemplated herein that additional auxiliarymonitoring fiber port 23 may be added in a similar fashion.

Potential limitations on the free space optics 74 and wavelengthswitching array 75 occur when configuring larger numbers of fibers thanthe present invention, if arranged along an optical axis of input fiberports 12, 14, 16, 18, and output fiber 64. Absent a fiber concentrator52, adding additional fibers makes it difficult to switch such increasednumber of fiber beams with such a large spacing between such fibersbecause the outermost fiber beams are so far off the center optical axiscapabilities of the mirrors in the preferred embodiment between inputfiber ports 16 and 18. Also, as discussed in more detail below, asignificant amount of optical magnification is required between thesefibers and the MEMS mirror array, and the MEMS design and function aregreatly simplified as a result of concentrating the fiber spacing.

Referring now to FIG. 7C, a schematically illustrated opticalconcentrator array 53 is shown wherein planar waveguides are included inthe 1×5 WXC according to an alternate embodiment of the presentinvention. Single-mode optical fibers 124 having cores 126 surrounded bycladdings 128 (shown in FIG. 7A) are butt coupled to concentrator 53.Illustrated in the 1×5 wavelength cross-connect switch 10.1 shown inFIG. 5A, one input port 12 and five output fiber ports 13, 15, 17, 19,21 are preferably optically coupled to fiber concentrator 53 in a linearalignment and are preferably optically coupled to fiber input port 12,and output fiber ports 13-21 to bring their beams closer together onoutput face 44 of fiber concentrator array 53 adjacent the optics, andto output the beams in parallel in a linearly spaced grid. Fiberconcentrator 53 preferably has curved shaped planar waveguides 32, 33,35, 37, 39, 47 and 49 within fiber concentrator 53 to preferablyconcentrate and reduce the spacing between fiber input fiber ports 12,13, 15, 17, 19, 21 from 125 micrometers, representative of the fiberdiameters, to the considerably reduced spacing of, for example, 30 or 40micrometers and preferably no more than 50 micrometers which is moreappropriate for the magnifying optics of switch 11 and an optimum sizeand spacing of the mirrors. Each of waveguides 33, 35, 37, 39, 47 ispreferably coupled to the respective input fiber port 12, and outputfiber ports 13, 15, 17, 19, 21. Further, waveguides 33, 35, 37, 39, 47preferably extend along a common plane directing the multi wavelengthbeams to output in free space and to propagate in patterns havingcentral axes which are also preferably co-planar.

FIG. 7C further discloses the fabricating of output taps 80 and planarwaveguide 49 into fiber concentrator 53 whereby taps 80 preferablycouple about 10% of the optical power from output fiber ports 13, 15,17, 19, 21 via waveguides 33, 35, 37, 39, 47 into planar waveguide 49,which directs the multi wavelength output beam to output in free spaceand to propagate in a pattern having a central axes which is preferablyco-planar with outputs from waveguides 32, 33, 35, 37, 39, 47 in freespace and switched by monitoring mirror array 73 (row B) after it haspassed through free space optics 74.

Concentrator 53 may include auxiliary monitoring fiber port 23, coupledto planar waveguide 43 wherein fiber concentrator 53 preferably outputsits multi-wavelength beam in free space propagating in a pattern havinga central axis which is preferably co-planar with outputs fromwaveguides 32, 33, 35, 37, 39, 47 in free space optics 74, therebyenabling an external multi-wavelength beam to be monitored by opticalswitching and monitoring system 10.1 or 11. An external signal not foundon input (N) may be input into auxiliary monitoring fiber port 23 andoptical switching and monitoring system 10.1 or 11 may be utilized tomonitor or read the power of each wavelength of a multi-wavelength beamon auxiliary monitoring fiber port 23 and to output such data to a userinterface (User i/f) port shown in FIGS. 5A and 5B. It is contemplatedherein that additional auxiliary monitoring fiber port 23 may be addedin a similar fashion.

Fiber concentrator 52 and 53 can be easily formed by a conventional ionexchange technique, such as is available from WaveSplitter Technologiesof Fremont, Calif. For example, waveguides 32, 34, 36, 38, 40, 41, 45,33, 35, 37, 39, 47, 49 are formed by doping such beam path to obtain ahigher refractive index than the surrounding undoped glass, and thus,can serve as optical waveguides. However, a half-elliptical shape isoptically disadvantageous. Therefore, after completion of ion exchange,a vertical electric field is applied to the substrate to draw thepositive ions into the glass substrate to create nearly circular dopedregions. These serve as the planar optical waveguides surrounded on allsides by the lower-index glass. Other methods are available for formingplanar waveguides.

Fibers 124 of FIGS. 7B and 7C are aligned to fiber concentrator 52 and53 at input face 127 of fiber concentrator 52 and 53. Preferably, thefiber end faces are inclined by about 8 degrees to the waveguides inorder to virtually eliminate back reflections onto fibers 124. Othertypes of concentrator chips and fiber holder substrates are available.

Fiber concentrator 52 and 53 preferably creates a relatively narrowspread of parallel free-space beams in a linear arrangement forwavelength cross-connect switch 10 and 11. Even when multiple fibers areconnected to wavelength cross-connect switch 10 and 11, the fiber beamsare concentrated to an overall width of only about 1 millimeter. Thedesign allows shorter focal length lenses and significantly reduces theoverall size of the package. It is also more reliable and highlytolerant to environmental stress than previously described systems.Without a concentrator, the number of fibers connected to wavelengthcross-connect switch 10 and 11 would be limited.

An example of front end optics 56 is illustrated in more detail in thecross-sectional view of FIG. 8. The free-space beams output by thewaveguides, whether planar or fiber, of fiber concentrator 52 or 53 aredivergent and form a curved field. This discussion will describe all thebeams as if they are input beams, that is, output from the concentratorto the free-space optics. The beams are in fact optical fields coupledbetween optical elements. As a result, the very same principles apply tothose of the beams that are output beams which eventually reenter fiberconcentrator 52 or 53 for transmission onto the network.

The beam output from fiber concentrator 52 or 53 enters into the crossconnect pass through field-flattening lens 220, in order to flatten whatwould otherwise be a curved focal plane of the collimator lens.Field-flattening lens 220 accepts a flat focal plane for the multipleparallel beams emitted from the concentrator. In the reverse direction,field-flattening lens 220 produces a flat focal plane and parallel beamscompatible with the end of the concentrator 42 to assure good couplingto waveguides in the concentrator.

In many optical systems, an image is formed on a curved, non-planarsurface, typically by beams non-parallel to each other. In manyapplications such as photographic imaging systems, such minor deviationsfrom a flat field are mostly unnoticeable and inconsequential. However,for a cross connect based on free-space optics, parallel single-modefibers, small parallel beams, and planar mirror arrays, a curved imagecan degrade coupling efficiency. Performance is greatly improved if theoptics produce a flat focal plane at output face 44, and on the returntrip it will be imaged onto fiber concentrator 52 or 53 waveguide ends.Hence, the ends of the input waveguides in fiber concentrator 52 or 53are imaged onto the ends of the output waveguides in fiber concentrator52 or 53, and the efficiency of coupling into the single-mode waveguidesstrongly depends on the quality of the image. Without thefield-flattening lens, it would be very difficult to build a WXC withmore than a few fiber ports because the error in focus wouldsignificantly increase for fibers displaced away from the optical axis.Field-flattening lens 220 preferably is designed as an optical elementwith negative focal length, and is thicker at its periphery than at itsoptical axis in the center. The basic function of the thicker glass atthe periphery is to delay the focus of the beams passing therein. Thedelayed focus serves to create a flat plane of focus points for allbeams, rather than a curved plane of foci that would occur otherwise. Afield-flattening lens may be implemented as a singlet lens, a doublet,aspheric, or other lens configuration.

A field-flattening lens may, in the absence of further constraints,produce an optical field in which the off-axis beams approach the flatfocal plane at angles that increasingly deviate from normal away fromthe optical axis. Such non-perpendicular incidence degrades opticalcoupling to fibers arranged perpendicular to the flat focal plane.Therefore, performance can be further improved if the beams are made toapproach the focal plane in parallel and in a direction normal to theflat focal plane. This effect of producing parallel beams is referred toas telecentricity, which is aided by long focal lengths.

After field-flattening lens 220, the beams pass through a collimatingdoublet lens 222, preferably consisting of concave lens 224 joined toconvex lens 226. Doublet lens 222 may be a standard lens such as ModelLAI-003, available from Melles Griot, which offers superior collimatingand off-axis performance. The effective focal length of the assembly maybe about 14 mm. Collimating lens 222 is illustrated as following thefield-flattening lens 220, which is preferred, but their positions canbe reversed with little change in performance.

As an aid to reducing the overall insertion loss of WXC in FIGS. 1, 2,4, 5 (although not a strict requirement), prism 228, which may be asimple wedge, preferably is placed between collimating lens 222 anddiffraction grating 62. Prism 228 pre-corrects for the astigmatismintroduced by diffraction grating 62. The wedge angle of the prism,along with the type of glass from which it is made, allows ellipticallyshaped (or astigmatic) beams to be created. If prism 228 is composed ofcommon optical glass, the wedge angle is typically on the order of 25degrees to compensate for the type of diffraction grating 62 consideredfor the invention. The ellipticity counteracts a similar ellipticitythat is an undesirable by-product of diffraction gratings. The netresult of the prism and grating is a distortion-free optical beam thatcan be efficiently processed by the remaining optical components in thesystem and ultimately coupled with high efficiency back into the smallcore of a single-mode fiber. Field-flattening lens 220, collimatingdoublet lens 222, and prism 228 are collectively and individuallyreferred to as front-end optics 56.

Referring now to FIG. 9A, a front face view of first channel MEMS mirror(row A) and five incident beams from the five fiber input fiber ports isillustrated, according to an illustrative embodiment of the presentinvention. Mirrors 72 and 73 (shown in FIG. 9B) of the mirror array arepreferably formed within a single substrate 264 (shown in FIG. 4) in arectangular two-dimensional array, which is arranged in a switching ormonitoring dimension and a wavelength dimension. A typical mirrorreflective surface 270 (shown in FIG. 4), is illustrated in the planview of FIGS. 9A, 9B, 9C includes switching mirror array 72 (row A)preferably having dimensions of about 200 micrometers in the x-axisdirection and about 250 micrometers in the y-axis direction. The opticsare designed to irradiate each mirror of switching mirror array 72,preferably with five elliptically shaped spots 320. As stated earlier,for example, λ1 mirror of switching mirror array 72 has λ1(12)-λ1(20)from all five input fiber ports 12-20 projected onto λ1 mirror surfacevia segmented prism element 68, and by tilting λ1 mirror of switchingmirror array 72 of switch 10 or 11, switches one selected λ1 (12-20)from fiber input fiber ports 12-20 to fiber output port 64 and drops theremaining unselected λ1(s) from input fiber ports 12-20, and so forthfor λ2-λn. In addition, the five elliptically shaped spots 320 are shownin a non-overlapping manner; however, spots 320 may overlap one anotheron each mirror of switching mirror array 72 (as shown in FIGS. 9C and12). λ1(12)-λ1(20) represented by spots 320 preferably have a diameteron an x-axis of about 100 micrometers and a diameter on a y-axis of 150micrometers. The MEMS mirrors of switching mirror array 72 preferablyspans about 10 millimeters in the x-axis direction (into the page inFIG. 2). It is contemplated by this invention herein that otherdimensions are feasible for switching mirror array 72.

Referring now to FIG. 9B, a front face view of a second channel MEMSmirror (row B) and two incident beams from the two monitoring inputfiber ports is illustrated according to an illustrative embodiment ofthe present invention. A typical mirror reflective surface 270 (shown inFIG. 4), is illustrated in the plan view of FIG. 9B includes monitoringmirror array 73 (row B) preferably having dimensions of 200 micrometersin the x-axis direction and 250 micrometers in the y-axis direction. Theoptics are designed to irradiate each mirror of monitoring mirror array73, preferably with two elliptically shaped spots 420. As statedearlier, for example λ1 mirror of monitoring mirror array 73 has λ1(21)and λ1(23) from two monitoring fiber ports 21 and 23 projected onto λ1mirror surface via segmented prism element 68, and by tilting λ1 mirrorof monitoring mirror array 73 switch 11 switches one selected λ frommonitoring fiber ports 21 or 23 to output monitoring fiber port 25 andblocks the remaining unselected λ from monitoring fiber ports 21 and 23as well as all other λs from monitoring fiber ports 21 and 23. Inaddition, the two elliptically shaped spots 420 are shown in anon-overlapping manner; however, spots 420 may overlap one another oneach mirror of monitoring mirror array 73. λ1(21) and λ1(23),represented by spots 420 preferably have a diameter on an x-axis about100 micrometers and a diameter on a y-axis of 150 micrometers. The MEMSmirrors of monitoring mirror array 73 span about 10 millimeters in thex-axis direction (into the page in FIG. 2). It is contemplated by thisinvention herein that other dimensions are feasible for monitoringmirror array 73.

Referring now to FIG. 9C, a front face view of third channel MEMS mirror72 (row A) and five incident beams from the five input fiber ports isillustrated, according to a preferred embodiment of the presentinvention. The five incident beams are preferably shown in anoverlapping manner.

Referring now to FIG. 10 there is a schematic illustration of a sixinput port by one output fiber port wavelength cross-connect switchdepicting an alternative prior art apparatus for accomplishing an N×1wavelength selective switch. The wavelength cross-connect switch of FIG.10 does not include a segmented prism element to focus the light beamsonto the MEMS mirror array. Rather, the wavelength cross-connect switchof FIG. 10 uses a simple lens (or lenses) in its back end optics. Suchan embodiment limits the wavelength cross-connect switch of FIG. 10 to asingle N×1 or 1×N architecture, and precludes use of multiple N×1 or 1×Nswitches in a single package, as shown in the other figures.Additionally, wavelength cross-connect switch of FIG. 10 employs a fibercollimating lens array (FCLA) 502 in place of a FCA and FE optics. TheFCLA 502 places a small collimating lens 504 at the output of eachfiber. This combination of FCLA 502 and collimating lens 504 generallyincreases the cost and complexity of the system, especially as morefibers are added, since each fiber requires a dedicated collimating lens504 with varying demanding alignment specifications.

Referring now to FIG. 11 there is an illustration of a typicalsingle-row MEMS mirror array λ1-λn, showing primary axis 506 andoptional secondary axis 508 of rotation. Each 1×N or N×1 switch in thepreferred embodiment uses one such row. A single MEMS chip may haveseveral such rows.

Referring now to FIG. 12 there is a three-dimensional schematic of aMEMS mirror of FIGS. 9A and 9C. As illustrated in FIG. 12 light beamsfrom/to the input/output fibers 1-7 preferably are all steered onto theswitching mirror array 72 by the SPE 68 (shown in FIGS. 1 and 2) in anoverlapping manner. The seven incident beams from the seven input fiberports are preferably shown in an overlapping manner. It should berecognized that rotation of λn mirror about its primary axis 506 couplesa selected λn by reflecting such selected λn to the output fiber 64(shown in FIGS. 1 and 2), and thus such rotation determines which λn isselected for monitoring or switching.

Referring now to FIG. 13 is a schematic illustration of a six input portby one output fiber port wavelength cross-connect switch representing anN×1 switch and is an alternative depiction of the preferred embodimentof the present invention shown in FIG. 1. This depiction emphasizes thepresent invention's ability to share all free space optics (FSO) 74,including front end optics (FE) 56, diffraction grating 62, back endoptics (BE) 66, segmented prism element (SPE) 68, and the elimination ofcollimating lenses 504 of FIG. 10.

Referring now to FIG. 14 there is a three-dimensional schematic of awavelength cross-connect switch according to an embodiment of thepresent invention. The wavelength cross-connect switch of FIG. 14 mayrepresent an N×1 or 1×N embodiment of the present invention.

Referring now to FIG. 15 there is a schematic illustration of a dualwavelength cross-connect switch 12 with SPE-based architecture forcreating manifold or multi-packaged switches within the same package.FIG. 15 uses the same ‘cutaway’ view as FIGS. 1 and 13 to illustrate anadvantage of the present invention's SPE-based architecture for creatingmanifold or multi-packaged switches within the same package, whilereaping the benefits of re-use of free space optics (FSO) 74 and MEMScontrol circuitry 78. By adding an additional row of mirrors 72.1 to theexisting switching mirror array 72, adding additional waveguides to FCA52, and adding additional facets to SPE 68, a dual or second N×1 switch10.3 is defined and is shown in the lower-left and upper-right parts ofFIG. 15. The wavelength cross-connect switches 10 and 10.3 of FIG. 15operate independently of one another (that is, their light paths do notinteract and such switches are capable of independent switching), whilesharing the same housing and common components. It should be recognizedthat SPE 68 is capable of refracting light beams at arbitrary angles;thus, allowing multiple steering points for λn, on multiple mirror rows,to exist. FIG. 15 illustrates a ‘cutaway’ view of one wavelength λn, andthat each MEMS mirror shown represents a row of mirrors coming out ofthe page, each mirror corresponding to a different wavelength λnseparated out by diffraction grating 62 and positioned by SPE 68.

Although this figure depicts two independent switches 10 and 10.3, theconcept can easily be extended to three, four, or an arbitrary number ofswitches by adding more rows of MEMS mirrors 72, more FCA 52 waveguides,and more SPE 68 facets. If desired, each N×1 or 1×N switch in thepackage can have a different value of ‘N’, down to N=1. Also, anyarbitrary combination of N×1 or 1×N configured switches can be used byaltering the external fibering. All of this is possible because of theSPE 68's ability to refract an arbitrary number of rays at arbitraryangles, although at some point of increasing the number of switches SPE68 may become impractically complex.

Use of common components by multiple internal N×1 or 1×N switchesenables advantages in physical size, thermal output, electrical powerconsumption, ease of manufacture, and materials and labor costs, whencompared to a solution involving multiple switches built and packagedindependently.

FIG. 16 illustrates the SPE-based architecture of the present invention,in combination with FCLA-based optics with lenslets 504 of FIG. 10. TheSPE architecture can be used with this type of optical input, as well asthe FCA 52 and FE 56 shown in FIGS. 1, 2, and 15. An advantage of thisapproach is that the complexity of SPE 68 is significantly reduced.

Referring now to FIGS. 17A AND 17B there is a schematic illustration ofan advantage of the present invention. FIG. 17A is prior art thatillustrates schematically a 4-input-fiber by 4-output-fiber opticalswitch, made up of four 1×N and four N×1 wavelength selectable switches.This is a common switch architecture used in telecom industry. In FIG.17B, is a schematic illustration of the same 4×4 switch 12, bututilizing an embodiment of the present invention of FIG. 15, wherein twoswitches are co-packaged in the same device. It should be recognizedthat the switch shown in FIG. 17B utilizes the advantages listed abovein the description of FIG. 15, compared to the “one-switch-per-device”architecture of FIG. 17A. Although both figures show a 4×4 switch, theconcept can easily be extended to any value of M×N. Likewise, althoughFIG. 17B illustrates two switches in each device, any number of switchescan be combined using the concept of the present invention. Othertelecom architectures that employ multiple optical switches, such asEast-West dual rings, can also benefit from the embodiments of thisinvention.

FIG. 18A is a schematic illustration of additional aspects andadvantages of the present invention. In this embodiment, SPE 68 isconstructed with prisms that direct beams to two rows of mirrors. Thelower row switching mirror array 72 is used to switch 5×1 signals asshown in FIG. 15. The upper row monitoring mirror array 73 is used toswitch 2×1 monitoring signals as a separate switch. The output of the2×1 monitoring switch is directed to a photodetector 79 serving as anintegrated optical power monitor (OPM). By sequentially switching eachmirror 73 in the array to send selected signal to photodetector 79,while dropping all other wavelengths, such switch obtains, in a shortperiod of time, the optical power of all wavelengths of monitoring fiberport 21. It is contemplated that optical switching and monitoring systemis capable of monitoring two fiber ports 21 and 23 sequentially, andthis concept is expandable to an arbitrary number of monitoring portsand/or wavelengths. Each wavelength of monitoring fiber port 21 ismonitored one at a time, by tilting monitoring mirror array 73 to thecorrect angle to couple its light into output monitoring fiber port 25from tap 81, wherein the tapped signal from output fiber port 64 iscoupled to monitoring fiber port 21. It should be recognized that a keyadvantage of using one WSX as a fiber switch, and the other as a channelselector for an OPM, is that the ‘sensor’ and ‘actuator’ of the opticalpower feedback loop are both contained in the same module, and benefitfrom re-use of internal components as described above.

Referring now to FIG. 18B there is a schematic illustration of apreferred embodiment of FIG. 3A, illustrating the design flexibilityafforded by SPE 68, wherein such SPE 68 is fabricating to have varyingrefraction angles (facet angles). Facet angles of deflection for thefive input fiber wavelengths, two input monitor fiber wavelengths, oneoutput monitoring fiber wavelength, and two output fiber wavelengthmodel preferably are 16.1, 13.3, 6.1, 2.8, 0.00, −2.8, −5.7, −6.5, −7.9degrees. The angles shown in this example correspond to the 5×1 plus 2×1embodiment shown in FIG. 18A.

Referring now to FIG. 19A, which illustrates the combination switch plusOPM of FIG. 18A, this time with the FCLA 502 and lenslet 504 asillustrated in FIG. 10.

Referring now to FIG. 19B there is illustrated a variation of FIG. 3A,illustrating the design flexibility afforded by SPE 68, by fabricatingthe SPE with arbitrary refraction angles. The angles shown in thisexample correspond to the 5×1 plus 2'1 embodiment shown in FIG. 19A. Itshould be recognized from FIGS. 3A, 18B, and 19B that SPE 68 is aversatile element that can be designed with an arbitrary set of prismsto accomplish refraction for a variety of embodiments and variations ofthe present invention. Both “FCA” plus “FE” type optical architecturescan also be accommodated; and arbitrary combinations of N×1 or 1×Nswitches can also be accommodated by changing the number of facetsand/or their refraction angles of SPE 68.

Referring now to FIG. 20 there is an illustration of a variation of FIG.19A, in which switching mirror array 72 operates a 1-input and 6-outputoptical switch. In order to monitor power on all fibers for control looppurposes, each output fiber port is tapped using taps 81 and fed to a6-in and 1-out switch co-packaged with the first switch. The 6-in and1-out switch sends its output to photodetector 79 for monitoring.Although it is not shown, the same concept could be applied to a WSXusing “FCA” plus “FE” type optical architecture, and to arbitrarynumbers of fibers.

Referring now to FIG. 21 there is a variation of FIG. 20, in which powercombiner 508 is used to combine all wavelengths from the six outputfiber ports, which are tapped using taps 81 and couples them tomonitoring fiber port 21. In this embodiment, the optical switching andmonitoring system has fewer ports than in the example of FIG. 20,possibly reducing the number of components simplifying the design.Although it is not shown, the same concept could be applied to a WSXusing “FCA” plus “FE” type optical architecture, and to arbitrarynumbers of fibers.

Referring now to FIG. 22A there is illustrated an alternative embodimentof the present invention. In FIG. 22A, one of the independent switchesis configured to accept M inputs and focus them onto one row of a firstswitching mirror array 72. Each mirror in switching mirror array 72 (onemirror per wavelength) tilts to select one of the inputs for reflectiononto a fixed (stationary) mirror 510, which can be patterned directlyonto SPE 68 or placed elsewhere in the system. Fixed mirror 510 reflectsthe signal onto one row of a second switching mirror array 72. Eachmirror in second switching mirror array 72.1 tilts to the anglenecessary to project its beam to the selected one of N outputs. Thesystem thus operates as an M-input by N-output switch, since any inputcan be coupled to any output. Although it is not shown, the same conceptcould be applied to a WSX using “FCA” plus “FE” type opticalarchitecture, and to arbitrary numbers of fibers. This alternativeembodiment of the present invention is different from the M×N opticalswitches described in U.S. Pat. No. 6,097,859 (Solgaard et al) becauseeach wavelength in the present invention can only exit the unit on oneoutput fiber at a time. In the referenced Solgaard patent, the M×Nestablishes multiple in-to-out paths on the same wavelength; however,the present invention teaches a simpler design, using fewer mirror rows,for example.

Also, in this and other inventions which incorporate two mirrors in thelight path, an additional advantage can be gained when using Pulse WidthModulated (PWM) signals to drive the mirrors, as described in U.S. Pat.No. 6,543,286 (Garverick, et al), U.S. Pat. No. 6,705,165 (Garverick, etal), and U.S. Pat. No. 6,961,257 (Garverick, et al). By operating eachof the two mirrors in the path with complementary pulse trains, anyinsertion loss (IL) ripple caused by mechanical vibration of the mirrorscan be reduced by operating each mirror with a complementary pulsetrain. This causes any mechanical vibration in one mirror to occur 180degrees out of phase with the other mirror, thus canceling IL ripple inthe optical signal.

Referring now to FIG. 22B there is illustrated an alternative embodimentof the present invention which accomplishes the same M×N switchingfunctionality of FIG. 22A. In this embodiment, there is no stationarymirror. Instead the input-side switch is configured as an N×1, and theoutput side as a 1×N. The output of the first switch is coupled to theinput of the second, either by fiber splicing, jumpering via fiberconnectors 83, on-chip patterning of waveguides, or the like. Althoughit is not shown, the same concept could be applied to a WSX using “FCA”plus “FE” type optical architecture, and to arbitrary numbers of fibers.This alternative embodiment of the present invention is different fromthe M×N optical switches described in U.S. Pat. No. 6,097,859 (Solgaardet al) because each wavelength in the present invention can only exitthe unit on one output fiber at a time. In the referenced Solgaardpatent, the M×N establishes multiple in-to-out paths on the samewavelength; however, the present invention teaches a simpler design,using fewer mirror rows, for example.

Referring now to FIG. 23 there is illustrated an alternative embodimentof the present invention. In FIG. 23 the switch is configured as twoidentical, independent switches. In this embodiment first and secondswitching mirror arrays 72 and 72.1 are operated such that they movesynchronously. Although it is not shown, the same concept could beapplied to a WSX using “FCA” plus “FE” type optical architecture, and toarbitrary numbers of fibers, numbers of co-packaged switches, andarbitrary port designations (input versus output).

With respect to the above description then, it is to be realized thatthe optimum dimensional relationships for the parts of the invention, toinclude variations in size, materials, shape, form, position, functionand manner of operation, assembly and use, are intended to beencompassed by the present invention. Moreover, where the references aremade to a 1×5 or 5×1 optical cross-connect switch, the concepts are alsoapplicable to other fiber counts such as 1×N, N×1 or N×N.

The invention disclosed and claimed relates to the various modificationsof assemblies herein disclosed and their reasonable equivalents, and notto any particular fiber count or wavelength count optical wavelengthcross-connect switch. Although the invention has been described withrespect to a wavelength cross connect, many of the inventive optics canbe applied to white-light optical cross connects that do not includewavelength dispersive elements. Although tilting micromirrors areparticularly advantageous for the invention, there are other types ofMEMS mirrors than can be electrically actuated to different positionsand/or orientations to affect the beam switching of the invention.

The foregoing description and drawings comprise illustrative embodimentsof the present invention. Having thus described exemplary embodiments ofthe present invention, it should be noted by those skilled in the artthat the within disclosures are exemplary only, and that various otheralternatives, adaptations, and modifications may be made within thescope of the present invention. Many modifications and other embodimentsof the invention will come to mind to one skilled in the art to whichthis invention pertains having the benefit of the teachings presented inthe foregoing descriptions and the associated drawings. Althoughspecific terms may be employed herein, they are used in a generic anddescriptive sense only and not for purposes of limitation. Accordingly,the present invention is not limited to the specific embodimentsillustrated herein, but is limited only by the following claims.

1. An optical system, comprising: at least one first moveable mirror forreceiving and reflecting at least one first selected wavelength from oneor more input fiber ports to one output fiber port according to aposition of said first mirror, said output fiber port transmitting anoutput optical signal of selected wavelengths from one or more inputoptical signals from said one or more input fiber ports; a tap forcoupling a portion of said output fiber port output optical signal to afirst monitoring port; at least one second moveable mirror for receivingand selectively reflecting at least one second selected wavelength fromsaid first monitoring port to an output monitoring port according to aposition of said second mirror; at least one steering element forsteering the first selected wavelength from each of said one or moreinput fiber ports onto said first mirror, and steering the firstselected wavelength from said first mirror to said output fiber port,and further steering the second selected wavelength from said firstmonitoring port onto said second mirror, and steering the secondselected wavelength from said second mirror to said output monitoringport; and an optical measurement device for receiving the secondselected wavelength of a portion of the output optical signal coupled tosaid output monitoring port and measuring at least one optical propertyof the output optical signal.
 2. The system of claim 1, wherein ameasurement by said optical measurement device is output from saidsystem.
 3. The system of claim 1, further comprising a controllerreceiving an output of said optical measurement device and responsivelyadjusting said position of said first mirror to effect control of saidmeasured property of said at least one first selected wavelength of saidoutput optical signal.
 4. The system of claim 3, comprising a pluralityof said first mirrors, a plurality of input optical signals from aplurality of said input fiber ports, and said optical measurement devicesequentially receiving a plurality of the second selected wavelength ofthe portion of the output optical signal and sequentially measuring atleast one optical property of said plurality of the second selectedwavelength, and wherein said controller adjusts said position of aplurality of said first mirror to effect control of said plurality ofthe first selected wavelength of the output optical signal.
 5. Thesystem of claim 1, further comprising a wavelength dispersive elementfor spatially separating each of the input optical signals into aplurality of spatially separated wavelengths.
 6. The system of claim 1,wherein said at least one first and at least one second moveable mirrorsare tiltable mirrors.
 7. The system of claim 6, wherein said tiltablemirrors are included in a micro electromechanical system array.
 8. Thesystem of claim 3, wherein said controller controls a switching routebetween said input fiber ports and said output fiber port by tiltingsaid at least one first mirror.
 9. The system of claim 3, wherein saidcontroller adjusts at least some of the power transmission coefficientsof the first selected wavelength of said output fiber port opticalsignal to be less than their maximum values.
 10. The system of claim 1,further comprising at least one auxiliary monitoring port, wherein saidat least one second moveable mirror selectively couples one wavelengthof said portion of said output fiber port output optical signal, or onewavelength of said at least one auxiliary monitoring port to said outputmonitoring port according to a position of said second mirror.
 11. Thesystem of claim 6, wherein said optical measurement device measures saidat least one optical property of each wavelength component of each saidoutput optical signal, and therefrom controls a tilting of said at leastone first mirror to effect a fractional change in power transmissionthrough said system.
 12. The system of claim 1, further comprising afiber port concentrator coupled to said one or more input port, said oneoutput fiber port, said first monitoring port, and said outputmonitoring port, wherein said fiber port concentrator optimizes theport-to-port spacing and outputs or receives the optical signals fromfree space in a predominately linearly spaced grid.
 13. The system ofclaim 12, wherein said tap is positioned within said fiber portconcentrator.
 14. The system of claim 1, further comprising opticswherein said optics focus the optical signals of said one or more inputports and said one output fiber port.
 15. The system of claim 1, furthercomprising front end optics, wherein the optical signals of said one ormore input ports and said one output fiber port are focused andcollimated thereby.
 16. The system of claim 1, further comprising backend optics, said back end optics steering and focusing the wavelengthfrom said input ports onto said mirror, and steering the selectedwavelength from said mirror to said one output fiber port.
 17. Thesystem of claim 1, further comprising a second monitoring port.
 18. Thesystem of claim 17, wherein said at least one second moveable mirror forreceiving and selectively reflecting the second selected wavelength fromsaid first or said second monitoring port to said output monitoring portaccording to a position of said second mirror.
 19. The system of claim18, wherein a measurement by said optical measurement device is outputfrom said system.
 20. The system of claim 1, wherein said steeringelement further comprises a monolithic element containing multipleprisms.
 21. The system of claim 1, wherein said steering element furthercomprises a monolithic element containing multiple lenses.
 22. Thesystem of claim 7, further comprising one or more optical systemscorresponding to the system of claim 7, wherein said systems are housedin a single manifold housing, and share said micro electromechanicalsystem array and said steering element.